1. Field of the Invention
The present invention is in the field of all-terrain vehicles, and more particularly relates to a personal all-terrain vehicle (ATV). Such vehicles are characterized as being of relatively small size and weight, and by being configured to carry one or two passengers who generally sit astride the vehicle in tandem, although some of these vehicles provide for the passenger(s) to sit partially within the vehicle. Such ATV's of the latter type generally have a bench style seat allowing the passenger and driver to sit side by side. Such vehicles are generally provided with four wheels having high-flotation tires, although some are provided with six or more such wheels and tires.
Further, such a vehicle may be configured also to carry a load, such as on a rack or on a load bed which is usually disposed at the rear of the vehicle. Some vehicles of this type have load racks both at the front and at the rear of the vehicle.
Additionally, such an ATV may have all-wheel-drive, or may have only an opposite pair of wheels which are driven. Vehicles of this type have become increasingly popular and are used for a wide range of purposes extending from recreation, to hunting, and to maintenance uses. Although some such ATV's may be amphibian, many are not. Although many such ATV's are not truly amphibian, they are intended to be able to and are used for making water crossings through a foot or so of water, as well as being able to negotiate deep mud.
Further to the above, the present invention relates to a drive train for such a vehicle and to a method of its operation.
2. Related Technology
Personal all-terrain vehicles (ATV's) of many different sizes, engine configurations, and engine types, as well as of differing drive train configurations, have been known for some time. Moreover, these conventional personal ATV's are generally recognized as including a single or multi-cylinder (usually a twin-cylinder) engine of horizontal shaft configuration, a multi-speed gear box transmission or a belt-type of continuously-variable transmission (CVT), and a power drive arrangement of one or more transfer cases and one or more differential cases providing power to an opposite pair or to all four wheels. Some ATV's also include a sub-transmission, allowing the operator to select from among two or more speed reduction (and traction power multiplication) ranges. The CVT's used in such ATV's is convention, and has received a high degree of development, starting generally with the use of such transmissions in snow mobiles.
Such CVT's generally include a first variable-diameter pulley assembly, which is engine driven, and is responsive to centrifugal force to act both as a clutch, and as a speed-responsive variable pulley. A belt is trained about this first pulley assembly, and extends to and around a second variable-diameter pulley assembly.
Generally, this second pulley assembly is torque responsive to cooperate with the first pulley assembly in establishing the effective speed and torque ratio between the driving pulley and the driven pulley.
A persistent problem with such ATV's which use a belt-type of CVT is that although the CVT is protected by a case, which is supposed to provide environmental and water protection to the drive belt and its variable pulleys, the severe use conditions to which many ATV's are subjected exceeds the protection provided to the CVT. Such is the situation particularly, when such conventional ATV's are subjected to use in making water crossings or are operated in deep mud. Such uses generally result in a great deal of moisture and water being around the CVT housing of the vehicle. In many cases some of the water or mud will find its way into the CVT transmission housing, and will get on the belt and/or pulleys of the CVT. Because such a CVT transmission depends for its proper operation upon the maintenance of a certain relatively high coefficient of friction between the rubber drive belt and the variable pulleys of the CVT transmission, when water or mud is introduced into such a transmission the power drive effectiveness of the vehicle may be largely lost.
Another consideration with conventional ATV's is that at higher speeds, the gyroscopic effect provided by the road wheels and tires contributes positively to vehicle stability. Conversely, when the vehicle is traveling at a relatively low ground speed, vehicle stability may not be as great as is desired. Even when the vehicle is traveling at a low ground speed, the engine and transmission components may be spinning at a high speed and will have a corresponding gyroscopic effect. That is, these engine and drive train components may have a significant gyroscopic effect which could contribute to vehicle stability. However, in conventional ATV's the gyroscopic effect of rotating components in the engine and drive train does not generally contribute positively to vehicle dynamics, or does not positively contribute to the full extent that would be possible. That is, a conventional ATV engine and transmission with horizontal shafts extending transversely to the vehicle can contribute a gyroscopic force which resists both roll and yaw, However, no effective gyroscopic effect is available to help stabilize the vehicle in pitch. Yet, because of their relatively short wheel base, stabilization of movements of a personal ATV in pitch is an important. aspect of vehicle stability and of driver and passenger comfort: on uneven terrain. Similarly, a conventional ATV with horizontal engine and transmission shafts extending longitudinally of the vehicle has gyroscopic forces which can assist vehicle stability in pitch and yaw, but not in roll. However, roll stability for such a vehicle is probably one of the most important stability considerations.
A conventional motor vehicle having all-wheel drive is disclosed in U.S. Pat. No. 751,540, issued Feb. 9, 1904 to D. L. McClintock (the '540 patent).
According to the '540 patent, a vehicle includes an engine with a horizontal shaft providing power into. a direction reversing gear box of T-configuration. As is seen in FIG. 10 of this patent, the T-configuration gear box may include a bevel gear power driven from the motor, and in constant mesh with an opposed pair of bevel gears. These opposed bevel gears are carried on a power output shaft, and are freely turning on this shaft. Each of the pair of opposed bevel gears defines a conical friction surface facing the like surface of the other of these pair of gears. Disposed between the pair of bevel gears is a double-sided friction cone, provided at its circumference with a groove into which a shift fork is received. This friction cone is drivingly but slidably related with the power output shaft. Accordingly, the output shaft may be power driven in each direction of rotation by selective engagement of the friction cone with a selected one of the opposed bevel gears by means of a shift lever connected to the shift fork.
Such T-configuration direction reversing gear units are known also which employ dog clutches rather than the conical friction clutch arrangements of the '540 patent. Such units are found, for example, in the lower drive units of outboard motors, in which they provide for selective forward and rearward driving of the boat propeller.
In view of the above, it would be desirable to provide an ATV having a drive train which is of increased resistance to being compromised by operation of the vehicle in water or deep mud. Similarly, it would be desirable to provide an ATV which utilized the gyroscopic forces available from spinning components in the engine and transmission system of the vehicle to improve vehicle stability and dynamics of movement at relatively low ground speeds.